Solar concentrators utilize lightweight, flexible reflective membranes to fabricate reflectors for focusing solar energy. A small negative pressure is applied to a cavity behind the reflective membrane, and the membrane is drawn into a curved configuration that approximates a paraboloid. When the reflector is pointed toward the sun, the solar radiation is concentrated at the focal point of the reflective membrane. The distance of the focal point depends upon the depth of curvature of the reflective membrane.
In one current design, 24 reflectors of 60-inch diameter each are mounted on a tracking structure to follow the relative movement of the sun. Solar energy is concentrated up to 5,000 times or more by the array of reflectors. Peak energy levels are in the order of 500 w/cm.sup.2 and are very destructive when directed onto objects not designed to draw the energy from the radiated surface. The intense heat flux must be removed quickly from a targeted device when any number of conditions arise. Examples of these conditions are when the application device experiences a failure or over-limit condition, electrical power to the concentrator controller and drive motors is lost, a component on the concentrator is damaged or fails which prevents proper tracking of the sun, concentrator limit sensors indicate a hazard condition, or when there is risk to human safety.
To safely operate solar concentrators using the flexible membrane design, schemes have been developed to reduce the concentrated energy levels. One scheme is to move the tracking structure away from the direction of the sun; this approach is effective if the target surfaces can withstand exposure while the tracking system articulates. For those targeted systems unable to deal with continued exposure, for conditions that prevent movement of the concentrator's drive mechanisms, or where equipment or human safety is endangered, a rapid defocusing system is needed.
Examples of prior art reflectors are disclosed in the following U.S. Pat. Nos. 4,422,723 to Williams, Jr. et al; 2,952,189 to Pajes; 4,033,676 to Brantley, Jr. et al; 3,514,776 to Mulready; 3,054,328 to Rodgers; 3,623,796 to Schweiger; 4,288,146 and 4,312,326 to Johnson, Jr.; and 4,548,482 to Williams, Jr. et al; and British patent 400,445 to Wurzburger, the disclosure of which are hereby incorporated herein by reference.
Thus, there is a continuing need to provide a rapid defocusing system for solar concentrators.